In the short span of five years, the Internet has changed inter-personal and inter-organizational communication. This phenomenon is largely the result of an open control language of protocol, the Internet Protocol (IP). The introduction of new control vocabularies and syntax, such as the Hypertext Transfer Protocol (HTTP), expanded the Internet into the World Wide Web (WWW), a multimedia communications distribution network with any-to-any connectivity. Other manifestations or generations of IP are evolving, which will have equally profound impact, such as one that is transforming the public switched telephone network (PSTN).
The command and control of the PSTN is built around a connection-oriented class structure. Call processing is completed by a complex array of switches, processors, and control networks, such as the Signaling System 7 or SS7. The PSTN is built on a class structure of specialized devices that perform single-purpose functions. For example, a Class 5 switch provides local access and call waiting; a Class 4 switch provides long distance, toll calls, and billing. Connectivity is also connection-oriented, where two devices must establish a discrete, deterministic connection or voice channel before communication can begin. The voice channel also must remain in place for the duration of the call. The PSTN is also a hierarchical one-to-many network that may result in traffic congestion, or blocking, thus creating the need for centralized control to proactively re-route the traffic. New service and feature development on this complex network is time consuming and strenuous, requiring 12-18 months of development. Service providers are spending billions of dollars annually to support this specialized infrastructure, as margin continues to erode and new development has stagnated.
The expanding interest in IP telephony has been driven by the opportunity to reduce network costs. IP-based communication is both classless and connectionless. IP networks deconstruct the class-based switch hierarchy into a powerful, any-to-any, class-independent network of packet transfer devices. Every packet of information carries all the necessary control information to “connect” the originating device to the destination device using only the needed resources. The convergence of transport and access networks, increased resource utilization through packet switching, and favorable regulatory conditions have propelled IP telephony to the top of many competitive service providers' network agenda. While technology cost reduction is still important, the competitive service providers have learned to focus on service differentiation in order to sustain competitive advantage. Service differentiation occurs at a high level than network interconnection. It requires transparent bridging of the media, control and application layers between IN (Intelligent Network) and IP networks.